1. Field of the Invention
The invention relates to a pinion assembly for differential gearing for an axle in a vehicle driveline.
2. Background Art
A driveline for an automotive vehicle typically comprises a driveshaft that is connected drivably to a geared differential drive pinion, usually a hypoid pinion, which engages a differential ring gear connected to a differential carrier. A differential carrier journals two or more pinions, which in turn drivably engage differential side gears. The side gears are connected to axle shafts for vehicle traction wheels.
The differential drive pinion includes a pinion shaft that is journaled by a pair of axially spaced bearings, usually tapered roller bearings, in a differential housing. A driving connection between an engine driven driveshaft and a drive pinion shaft is achieved by using a universal coupling, which may have constant velocity characteristics if the centerline of the driveshaft is disposed with respect to the centerline of the pinion at an angle greater than a predetermined amount. The universal coupling comprises a flange, including a drive pinion flange in a plane that is perpendicular with respect to the centerline of the drive pinion shaft. The flange includes a flange hub that is internally splined to permit a driving connection between the flange hub and an externally splined portion of the drive pinion shaft. The flange is secured to the drive pinion shaft by a locknut that is threaded on an end of the shaft. Typically, the locknut engages a hub of the flange.
Driveline vibrations often occur due to a so-called “runout” of the drive pinion flange due to radial displacement of the rotational axis of the drive pinion shaft with respect to the center of the universal coupling for the driveshaft. A flange runout may occur also in an axial direction due to flange surface variations, variations in pitch diameter of the drive pinion, variable tolerances of drive pinion shaft bearings and variations in the squareness of other rotary elements of the assembly, such as a washer or “oil slinger” with which the flange is engaged. The axial runout, together with the radial runout of the pinion shaft axis, produce a so-called composite runout, which is a vector sum of radial and axial runout components.
Composite runout can be measured by a master fixture that may be attached to the drive pinion shaft flange prior to final assembly. Other methods, such as a laser measurement technique of the flange itself, also may be used. The laser technique would eliminate machining errors in the master fixture, thus providing a more accurate measurement.
Typically, the drive pinion flange spline is characterized by a high press fit. Spline errors in a typical design can cause the flange to orient itself in a random fashion. An error caused by variations in the spline fit is a major contributor to composite flange runout. The other contributors to composite flange runout are errors measured at the flange face, at a flange pilot and at a flange locknut face, as well as at the flange surface that contacts the locknut face.